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Programming
program, , showing programming– if the white bishop at b3 moves to a2, capturing the black knight, then the black pawn at b1 is programmed to capture the bishop back. Black has just moved a pawn to c2.}} Computer programming is the process of designing and building an for accomplishing a specific task. Programming involves tasks such as: analysis, generating s, profiling algorithms' accuracy and resource consumption, and the implementation of algorithms in a chosen (commonly referred to as coding). The of a program is written in one or more languages that are intelligible to s, rather than , which is directly executed by the . The purpose of programming is to find a sequence of instructions that will automate the performance of a task (which can be as complex as an ) on a computer, often for solving a given problem. The process of programming thus often requires expertise in several different subjects, including knowledge of the , specialized algorithms, and formal . Tasks accompanying and related to programming include: , , maintenance, implementation of , and management of derived , such as the of computer programs. These might be considered part of the programming process, but often the term is used for this larger process with the term programming, implementation, or coding reserved for the actual writing of code. combines techniques with software development practices. is the opposite process. A is any skilled computer expert that uses their technical knowledge to overcome a problem, but it can also mean a in common language. History , whose notes added to the end of 's paper included the first designed for processing by an . She is often recognized as history's first computer programmer.}} Programmable devices have existed at least as far back as 1206 AD, when the of were programmable, via pegs and s, to play various rhythms and drum patterns; and the 1801 could produce entirely different weaves by changing the "program" - a series of cards with holes punched in them. However, the first computer program is generally dated to 1843, when mathematician published an to calculate a sequence of , intended to be carried out by 's . s, which were kept in order and arranged in program decks.}} In the 1880s invented the concept of storing data in machine-readable form. Later a (plugboard) added to his 1906 Type I Tabulator allowed it to be programmed for different jobs, and by the late 1940s, such as the and , were programmed by control panels in a similar way; as were the first s. However, with the concept of the s introduced in 1949, both programs and data were stored and manipulated in the same way in . was the language of early programs, written in the of the particular machine, often in notation. s were soon developed that let the programmer specify instruction in a text format, (e.g., ADD X, TOTAL), with abbreviations for each operation code and meaningful names for specifying addresses. However, because an assembly language is little more than a different notation for a machine language, any two machines with also have different assembly languages. .}} s made the process of developing a program simpler and more understandable, and less bound to the underlying hardware. , the first widely used high-level language to have a functional implementation, came out in 1957 and many other languages were soon developed – in particular, aimed at commercial data processing, and for computer research. Programs were mostly still entered using punched cards or . See . By the late 1960s, and became inexpensive enough that programs could be created by typing directly into the computers. were developed that allowed changes and corrections to be made much more easily than with punched cards. Modern programming Quality requirements Whatever the approach to development may be, the final program must satisfy some fundamental properties. The following properties are among the most important: * : how often the results of a program are correct. This depends on conceptual correctness of algorithms, and minimization of programming mistakes, such as mistakes in resource management (e.g., s and s) and logic errors (such as division by zero or s). * : how well a program anticipates problems due to errors (not bugs). This includes situations such as incorrect, inappropriate or corrupt data, unavailability of needed resources such as memory, operating system services and network connections, user error, and unexpected power outages. * : the of a program: the ease with which a person can use the program for its intended purpose or in some cases even unanticipated purposes. Such issues can make or break its success even regardless of other issues. This involves a wide range of textual, graphical and sometimes hardware elements that improve the clarity, intuitiveness, cohesiveness and completeness of a program's user interface. * : the range of and platforms on which the source code of a program can be / and run. This depends on differences in the programming facilities provided by the different platforms, including hardware and operating system resources, expected behavior of the hardware and operating system, and availability of platform specific compilers (and sometimes libraries) for the language of the source code. * : the ease with which a program can be modified by its present or future developers in order to make improvements or customizations, fix and , or adapt it to new environments. Good practices during initial development make the difference in this regard. This quality may not be directly apparent to the end user but it can significantly affect the fate of a program over the long term. * / : Measure of system resources a program consumes (processor time, memory space, slow devices such as disks, network bandwidth and to some extent even user interaction): the less, the better. This also includes careful management of resources, for example cleaning up s and eliminating s. Readability of source code In computer programming, refers to the ease with which a human reader can comprehend the purpose, , and operation of source code. It affects the aspects of quality above, including portability, usability and most importantly maintainability. Readability is important because programmers spend the majority of their time reading, trying to understand and modifying existing source code, rather than writing new source code. Unreadable code often leads to bugs, inefficiencies, and . A study found that a few simple readability transformations made code shorter and drastically reduced the time to understand it. Following a consistent often helps readability. However, readability is more than just programming style. Many factors, having little or nothing to do with the ability of the computer to efficiently compile and execute the code, contribute to readability. Some of these factors include: *Different s (whitespace) * * * for objects (such as variables, classes, procedures, etc.) The aspects of this (such as indents, line breaks, color highlighting, and so on) are often handled by the , but the content aspects reflect the programmer's talent and skills. Various s have also been developed with the intent to resolve readability concerns by adopting non-traditional approaches to code structure and display. s (IDEs) aim to integrate all such help. Techniques like can enhance readability. Algorithmic complexity The academic field and the engineering practice of computer programming are both largely concerned with discovering and implementing the most efficient algorithms for a given class of problem. For this purpose, algorithms are classified into orders using so-called , which expresses resource use, such as execution time or memory consumption, in terms of the size of an input. Expert programmers are familiar with a variety of well-established algorithms and their respective complexities and use this knowledge to choose algorithms that are best suited to the circumstances. Chess algorithms as an example "Programming a Computer for Playing Chess" was a 1950 paper that evaluated a "minimax" that is part of the history of algorithmic complexity; a course on IBM's is part of the computer science curriculum at . Methodologies The first step in most formal software development processes is , followed by testing to determine value modeling, implementation, and failure elimination (debugging). There exist a lot of differing approaches for each of those tasks. One approach popular for requirements analysis is analysis. Many programmers use forms of where the various stages of formal software development are more integrated together into short cycles that take a few weeks rather than years. There are many approaches to the Software development process. Popular modeling techniques include Object-Oriented Analysis and Design ( ) and Model-Driven Architecture ( ). The Unified Modeling Language ( ) is a notation used for both the OOAD and MDA. A similar technique used for database design is Entity-Relationship Modeling ( ). Implementation techniques include imperative languages ( or ), , and . Measuring language usage It is very difficult to determine what are the most popular of modern programming languages. Methods of measuring programming language popularity include: counting the number of job advertisements that mention the language, the number of books sold and courses teaching the language (this overestimates the importance of newer languages), and estimates of the number of existing lines of code written in the language (this underestimates the number of users of business languages such as COBOL). Some languages are very popular for particular kinds of applications, while some languages are regularly used to write many different kinds of applications. For example, is still strong in corporate data centers often on large s, in engineering applications, s in development, and in . Many applications use a mix of several languages in their construction and use. New languages are generally designed around the syntax of a prior language with new functionality added, (for example adds object-orientation to C, and adds memory management and to C++, but as a result, loses efficiency and the ability for low-level manipulation). Debugging from 1947 which is at the origin of a popular (but incorrect) etymology for the common term for a software defect.}} Debugging is a very important task in the software development process since having defects in a program can have significant consequences for its users. Some languages are more prone to some kinds of faults because their specification does not require compilers to perform as much checking as other languages. Use of a tool can help detect some possible problems. Normally the first step in debugging is to attempt to reproduce the problem. This can be a non-trivial task, for example as with parallel processes or some unusual software bugs. Also, specific user environment and usage history can make it difficult to reproduce the problem. After the bug is reproduced, the input of the program may need to be simplified to make it easier to debug. For example, a bug in a compiler can make it crash when parsing some large source file. However, after simplification of the test case, only few lines from the original source file can be sufficient to reproduce the same crash. Such simplification can be done manually, using a divide-and-conquer approach. The programmer will try to remove some parts of original test case and check if the problem still exists. When debugging the problem in a GUI, the programmer can try to skip some user interaction from the original problem description and check if remaining actions are sufficient for bugs to appear. Debugging is often done with s like , , , , and . Standalone debuggers like are also used, and these often provide less of a visual environment, usually using a . Some text editors such as allow GDB to be invoked through them, to provide a visual environment. Programming languages Different programming languages support different styles of programming (called s). The choice of language used is subject to many considerations, such as company policy, suitability to task, availability of third-party packages, or individual preference. Ideally, the programming language best suited for the task at hand will be selected. Trade-offs from this ideal involve finding enough programmers who know the language to build a team, the availability of compilers for that language, and the efficiency with which programs written in a given language execute. Languages form an approximate spectrum from "low-level" to "high-level"; "low-level" languages are typically more machine-oriented and faster to execute, whereas "high-level" languages are more abstract and easier to use but execute less quickly. It is usually easier to code in "high-level" languages than in "low-level" ones. , in his book,"How To Think Like A Computer Scientist", writes: :The details look different in different languages, but a few basic instructions appear in just about every language: :*Input: Gather data from the keyboard, a file, or some other device. :*Output: Display data on the screen or send data to a file or other device. :*Arithmetic: Perform basic arithmetical operations like addition and multiplication. :*Conditional Execution: Check for certain conditions and execute the appropriate sequence of statements. :*Repetition: Perform some action repeatedly, usually with some variation. Many computer languages provide a mechanism to call functions provided by . Provided the functions in a library follow the appropriate run-time conventions (e.g., method of passing ), then these functions may be written in any other language. References